ixgbe: Reduce memory consumption with larger page sizes

The ixgbe driver allocates pages for its receive rings. It currently
uses 512 pages, regardless of page size. During receive handling it
adds the unused part of the page back into the rx ring, avoiding the
need for a new allocation.

On a ppc64 box with 64 threads and 64kB pages, we end up with
512 entries * 64 rx queues * 64kB = 2GB memory used. Even more of a
concern is that we use up 2GB of IOMMU space in order to map all this
memory.

The driver makes a number of decisions based on if PAGE_SIZE is less
than 8kB, so use this as the breakpoint and only allocate 128 entries
on 8kB or larger page sizes.

Signed-off-by: Anton Blanchard <anton@samba.org>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>